To reduce the widespread death and disease that results from cigarette smoking, declines in prevalence must accelerate. Prescription medications to aid quitting can be effective, but up to 80% of smokers who attempt to quit do so without medical assistance. The U.S. Department of Health and Human Services promotes exercise as an aid for quitting, however, there are significant gaps in our understanding of how exercise is helpful. To date, aerobic exercise has been the only type of exercise investigated; there is a poor understanding of the mechanisms of action; and there is an under-representation of male smokers in the literature. This trial is designed to produce new data that will address each of these gaps. Positive results from our pilot study [R03 CA132475] suggest that resistance training (i.e., weight training) can offer smokers a unique behavioral strategy for quitting. When compared to a control, resistance trained participants were more likely to achieve smoking abstinence and have lower body weight and body fat at the end of the trial. This is a key benefit, as the body weight/fat gain that typically occurs during and after quitting offsets th benefit of cessation with significant increases in the risks for type 2 diabetes, hypertension, and a decline in lung function. The purpose of this study is to test of the efficacy of resistance training as an aid to smoking cessation in the first full scale randomized controlled trial. A tota of 206 male and female smokers will receive a brief smoking cessation counseling session prior to being randomized into a 12-week Resistance Training or Contact Control group. Both groups will meet on-site twice per week during the 12-week program, and follow-up assessments will occur at the end of the 12-weeks (3-month) and at a 6-month and 12-month time point. Participants will not receive any additional smoking cessation treatment during follow-up; however, the Resistance Training group will receive a 9-month membership to a fitness center to encourage continued resistance training as a way to maintain cessation, and attendance to the center will be tracked. Participants in the Contact Control group will also receive a 9-month fitness center membership after their 12-month follow-up. The primary outcome is salivary cotinine verified 7-Day Point Prevalence Abstinence (PPA) at the 3-month assessment, and at the 6 and 12-month follow-ups. Secondary outcomes will include an examination of (a) the potential mechanisms of action (e.g., acute changes in cortisol, mood, cravings, abstinence self-efficacy, sleep) assessed during the 12-week intervention; (b) treatment differences on biological markers of disease risk (e.g., lung function, HbA1c, blood lipids, body composition, bone mass, blood pressure), physical fitness, and exercise behavior at each follow-up; and (c) the association between each of these variables and smoking outcomes. Finally, we will explore whether gender moderates the effect of treatment on smoking outcome, or on any of the other dependent variables (e.g., mechanisms of action, biological markers, fitness, exercise behavior).